1. Field Of The Invention
The present invention relates to a curable polyphenylene ether resin composition, a cured polyphenylene ether resin composition, a laminate structure and a composite structure. More particularly, the present invention is concerned with a curable polyphenylene ether resin composition comprising a curable polyphenylene ether resin having at least one group selected from the group consisting of an allyl group and a propargyl group, and at least one cyanurate. Also, it is concerned with a cured polyphenylene ether resin composition comprising a chloroform nonextractable polyphenylene ether resin component and a chloroform extractable, polyphenylene ether-containing component obtained by curing the above-mentioned curable polyphenylene ether resin composition. Further, it is concerned with a laminate structure comprising a metallic foil and at least one cured resin composition layer disposed on at least one surface of said metallic foil, and a composite structure comprising a metallic substrate and at least one cured resin composition layer disposed on at least one surface of the metallic substrate.
The curable polyphenylene ether resin composition of the present invention has excellent storage stability, film forming properties and melt moldability, and the cured polyphenylene ether resin composition of the present invention has excellent chemical resistance, electrical properties (such as low dielectric constant and low dielectric dissipation factor), fire retardance, dimensional stability and heat resistance. Accordingly, the cured polyphenylene ether resin composition can advantageously be used as a dielectric material, an insulating material, a heat resistant material and the like in, for example, electrical and electronic industries, space and aircraft industries, etc.
The laminate structure and composite structure of the present invention can advantageously be used as a single-sided printed circuit board, a double-sided printed circuit board, a multi-layer printed circuit board, a flexible printed circuit board and the like.
2. Discussion Of Related Art
In recent years, miniaturization and high-packing-density mounting have been strongly desired in the field of electronic devices for communication, household, industries and the like. Accordingly, materials for such devices having excellent heat resistance, dimensional stability and electrical properties have been strongly desired in the art. For example, a copper-clad laminate made of a substrate comprising a thermosetting resin, such as a phenol resin and an epoxy resin, has been used as a printed circuit board. However, such a thermosetting resin has a drawback in that the resin has undesirable electrical properties, particularly an undesirably high dielectric constant in a high frequency range, although the resin has a good balance of various properties.
For overcoming the above-mentioned drawback, polyphenylene ether has been attracting attention as a new material, and it has been attempted to apply a polyphenylene ether to a copper-clad laminate. Indeed, a polyphenylene ether is one of the typical engineering plastics which has not only excellent mechanical but also desired electrical properties, such as a low dielectric constant and a low dielectric dissipation factor, and has also a relatively good heat resistance. However, when a polyphenylene ether is used as a material for a printed circuit board substrate, the heat resistance thereof is insufficient. A material for a printed circuit board substrate is required to have an extremely high heat resistance, because a printed circuit board substrate is necessarily exposed to high temperatures in soldering. However, substrates made of conventional polyphenylene ethers are likely to undergo distortion at temperatures higher than about 200.degree. C., thereby causing a considerable decrease in mechanical properties and peeling off of copper foils provided as circuits on the surface of the substrate. A polyphenylene ether has also another drawback in that it has such poor resistance to an aromatic hydrocarbon and a hydrocarbon substituted with a halogen atom that it is ultimately dissolved in such hydrocarbons, although the polyphenylene ether has excellent resistance to acids, alkalis and hot water.
For improving the heat resistance and chemical resistance of a polyphenylene ether, various proposals have been made, in which a polyphenylene ether is formulated into a composition. For example, Japanese Patent Application Laid-Open Specification No. 61-287739 discloses a composite structure comprising as a resin substrate a cured resin obtained by curing a resin composition comprising a polyphenylene ether and at least one member selected from the group consisting of triallyl cyanurate and triallyl isocyanurate. The cured resin has poor chemical resistance, e.g., poor resistance to boiling trichloroethylene, and poor fire retardance, so that the composite structure is not suited for use as a printed circuit board. In a method comprising preparing a solution of the resin composition and fabricating the solution into a film according to a casting method, the resin composition solution has poor film-forming properties, so that disadvantageously it is difficult to obtain a film with a smooth surface. This reference does not teach or suggest a polyphenylene ether having an ethylenically or acetylenically unsaturated group, such as an allyl group or a propargyl group, which can provide, in cooperation with a triallyl cyanurate or isocyanurate, an advantageous curable polyphenylene ether resin composition as described below in the present invention.
U.S. Pat. No. 3,557,045 discloses a thermosetting resin composition comprising (a) 5 to 95% by weight of a polymerizable material containing carbon-carbon double bonds, at least 5% of which is a liquid monomer, (b) 95 to 5% by weight of a polyphenylene ether resin, and (c) a radical initiator. In particular, the patent discloses a composition comprising a diallyl phthalate monomer, a diallyl phthalate prepolymer, a polyphenylene ether resin and a radical initiator, which composition is described as having improved electrical and mechanical properties. This composition, however, has poor chemical resistance. In the patent, there is no description teaching or suggesting a composition comprising a polyphenylene ether and triallyl cyanurate or triallyl isocyanurate as described below.
U.S. Pat. No. 3,637,578 discloses a thermosetting resin composition comprising (a) 10 to 95% by weight of a mixture of a liquid monomer containing carbon-carbon double bonds in an amount of at least 5% and having a boiling point of 70.degree. C. or higher with a reactive polyester resin, (b) 5 to 90% by weight of a polyphenylene ether resin and (c) a radical initiator. It is described that the thermosetting resin composition can be cured to obtain a thermoset resin having improved electrical and mechanical properties. In Examples 3-2 and 3-4, a composition comprising a polyphenylene ether resin, a polyester resin, triallyl cyanurate and diallyl phthalate is disclosed. The polyphenylene ether resin content of the composition is 20%, with the balance of 80% being comprised of crosslinkable components (i.e., polyester resin, triallyl cyanurate and diallyl phthalate). However, the chemical resistance of this thermoset resin is not sufficient. This reference does not teach or suggest a polyphenylene ether having an ethylenically or acetylenically unsaturated group, such as an allyl group or a propargyl group, which can provide in cooperation with triallyl cyanurate or isocyanurate, an advantageous curable polyphenylene ether resin composition as described below in the present invention.
U.S. Pat. No. 3,936,414 discloses a thermosetting composition comprising (a) 10 to 50 parts by weight of a polyunsaturated monomer, (b) 5 to 30 parts by weight of a polychlorinated or polybrominated aromatic hydrocarbon having a molecular weight of at least 200 and a chlorine or bromine content of at least 50% by weight, (c) 20 to 60 parts by weight of a polyphenylene ether, (d) 0 to 30 parts by weight of a polyunsaturated polymer having unsaturated carbon-carbon bonds and (e) 2 to 10 parts by weight, per 100 parts by weight of components (a)+(b)+(c)+(d), of a peroxide. Examples of polyunsaturated monomers (a) include triallyl cyanurate and triallyl isocyanurate. However, the chemical resistance of this composition is not satisfactory, so that the practical use of the composition is limited. This reference does not teach or suggest a polyphenylene ether having an ethylenically or acetylenically unsaturated group, such as an allyl group or a propargyl group, which can provide, in cooperation with triallyl cyanurate or isocyanurate, an advantageous curable polyphenylene ether resin composition as described below.
On the other hand, with respect to general-purpose printed circuit boards comprising a glass fiber-reinforced epoxy resin substrate, various proposals have also been made to improve the heat resistance and electrical properties thereof. For example, it was proposed to improve the heat resistance and electrical properties of such printed circuit boards by employing a resin blend comprising a polyphenylene ether and an epoxy resin. In this connection, reference is made to Japanese Patent Application Laid-Open Specification No. 58-69052/1983 and Japanese Patent Application Publication No. 64-3223/1989, in which a composite structure comprising a resin layer comprised of a polyphenylene ether and an epoxy resin and a glass fabric is disclosed. The chemical resistance of the resin layer of the composite structure is not satisfactory, and hence the composite structure is not suitable for use as a printed circuit board.